We propose to study host regulation of spontaneous leukemia in inbred strains of laboratory mice, through a multidisciplinary approach involving analysis of genetic control of virus expression, arrangemnt of viral nucleic acid sequences in cellular DNA and cellular immunologic activity to virus and tumor antigens. We plan to examine neonatal expression of ecotropic virus infection in hybrids of AKR mice in relation to cellular immunity to virus and leukemogenesis. The technique of restriction endonuclease digestion and DNA blotting will be used to analyze spontaneous virus expression in murine cells, the Fv-1 genetic restriction, chromosomal localization of viral DNA sequences using somatic cell hybrids, and sequence arrangement in thymoma cell cultures. We plan to learn whether immunological tolerance to virus antigens may influence leukemia development, and whether viral immunologic suppressor or enhancing activity may exist under certain conditions.